I agree with much of what Kevin Drum has to say about the notion that the economy is being held back by a mysterious increase in “uncertainty.”
But a deeper lancing of this particular boil starts with the observation that it’s totally unclear what’s supposed to make this different from the standard Keynesian diagnosis. Indeed, Keynes himself put uncertainty front and center in his diagnosis of the business cycle and more modern “Keynesian” accounts tend to leave it out because it’s (a) hard to model and (b) not clear what difference it makes (see Brian Weatherson, “Keynes, Uncertainty, and Interest Rates” [PDF]).
Policymakers can’t make it cease to be the case that the future is uncertain. Policymakers can observe, however, that if economic actors’ level of uncertainty about the future increases that would manifest itself as an increased demand for money. Increased demand for money is a funny beast. Normally if demand for one kind of good or service falls, demand for other goods or services has to rise. But if what people demand is money itself then we find ourselves mired in a general glut, a shortfall of aggregate demand. Which is to say you’d be in just the normal Keynesian situation and you’d want to get out of it in just the normal Keynesian way — looser monetary and fiscal policy to bolster aggregate demand, soak up the excess capacity, and return us to a low-idleness equilibrium.
So if for whatever reason businessmen or politicians or media figures or anyone else feels more comfortable expressing the situation as one caused by “uncertainty” that’s fine. But the name of the game is still fiscal and monetary expansion. But instead the proposed cure typically seems to be “shift public policy in a more rightwing direction.” That wouldn’t do anything about uncertainty or a shortfall in aggregate demand. It’s just a faux-sophisticated way of saying “I’m a rich businessman who wants politicians to cater to my interests more.”